How to check if a file contains only zeros in a Linux shell?

Question

How to check if a large file contains only zero bytes (\'\\0\') in Linux using a shell command? I can write a small program for this but this seems to be an ov

Answer 1

It won't win a prize for elegance, but:

xxd -p file | grep -qEv '^(00)*$'

xxd -p prints a file in the following way:

23696e636c756465203c6572726e6f2e683e0a23696e636c756465203c73
7464696f2e683e0a23696e636c756465203c7374646c69622e683e0a2369
6e636c756465203c737472696e672e683e0a0a766f696420757361676528
63686172202a70726f676e616d65290a7b0a09667072696e746628737464
6572722c202255736167653a202573203c

So we grep to see if there is a line that is not made completely out of 0's, which means there is a char different to '\0' in the file. If not, the file is made completely out of zero-chars.

(The return code signals which one happened, I assumed you wanted it for a script. If not, tell me and I'll write something else)

EDIT: added -E for grouping and -q to discard output.